Capcitor transient problem

1. The problem statement, all variables and given/known data
Ok so I have attached the question im working on.
Basically when I have the circuit before or after switching in steady state I believe the current will equal zero. However if this is the case, how do I determine what happens immediately after switching?

Staff: Mentor

1. The problem statement, all variables and given/known data
Ok so I have attached the question im working on.
View attachment 52539
Basically when I have the circuit before or after switching in steady state I believe the current will equal zero. However if this is the case, how do I determine what happens immediately after switching?

Staff: Mentor

That may be true, but it's not relevant to the solution really. What is i(0+)?

Can you visualize what happens? Some initial current flows based on the initial voltage and the resistance, and that current decays according to the equation. And since you correctly calculated tau as 1 second, and they ask for something after 1 second, can you guess the answer?

Staff: Mentor

Ok so the initial current immediately after switching will be 12mA?
Therefore B will equal 12x10-3?
Thus i(t) = 12x10-3e-t?

You left the time constant divider out of the exponent. Even though it is "1", you should still show something there to show that the units work. So you could put a 1s in the denominator of the exponential term, for example. Other than that, it looks good. What is the answer at 1 second?